Mechanical behavior and microstructural analysis of alumina–titanium brazed interfaces

The ceramic–metal joints for electrical and vacuum engineering devices require high-density alumina ceramic and low glass phase content. Consequently it is necessary to introduce variations in the standard method of metallizing. Our assembly was designed to minimize the difference of thermal expansion between the alumina ceramic and titanium flanges, and was composed by alumina part/Mo–Mn film/Ag–Cu brazing alloy/Ni layer/titanium part. Its transversal section was observed by SEM and analyzed by scanning EDS. The assembly was submitted to the traction test to obtain σ × ɛ curves to study the mechanical behavior. SEM and EDS results indicated that the alumina superficial pores were filled out by molybdenum resulting in a mechanical bonded interface. In the same way, the copper from Ag–Cu brazing alloy filled in the pores of the Mo–Mn layer, modifying the original brazing alloy composition. The fracture occurred in the ceramic part and this was related to the formation of the Al2[(Mo, Mn)O4]3 crystalline phase in the alumina—Mo–Mn interface, which contributes to the increase of the adherence of the metallic layer to the ceramic. The mechanical resistance of the interface between the Ag–Cu brazing alloy and Mo–Mn layer is increased by the diffusion of copper.